1. Field of the Invention
This invention relates to the use of chelating molecules to deactivate iron and other transition metal species to prevent fouling in hydrocarbon fluids. Specifically, the invention relates to the use of Mannich reaction products of catechols with various polyamines as deactivating compounds.
2. Description of the Prior Art
In a hydrocarbon stream, saturated and unsaturated organic molecules, oxygen, peroxides, and metal compounds are found. Transition metal compounds such as iron can initiate fouling in three ways. First, they can interact with peroxides by catalyzing free radical formation and subsequent fouling. Second, metal species can complex oxygen and catalyze the formation of peroxides. Last, metal compounds can react directly with organic molecules to yield free radicals.
The first row transition metal species manganese, iron, cobalt, nickel, and copper are found in trace quantities (0.01 to 100 ppm) in crude oils. These metal species are carried over to hydrocarbon streams that are being refined, and in refined products with additional ions. C. J. Pedersen (Inc. Eng. Chem., 41,924-928, 1949) showed that these transition metal species reduce the induction time for gasoline, and indication of free radical initiation. Iron compounds are more likely to initiate free radicals than the other first row transition elements under these conditions.
To counteract the free radical initiating tendencies of the transition metal species and, in particular, iron, so called metal deactivators are added to hydrocarbons with transition metal species already in the hydrocarbon. These materials typically are organic chelators which tie up the orbitals on the metal rendering the metal inactive. When metal species are deactivated, fewer free radicals are initiated and smaller amounts of antioxidants are required to inhibit polymerization. However, not all chelators will function as metal deactivators. In fact, some chelators will act as metal activators. Pedersen showed that while copper is deactivated by many chelators, other transition metals are only deactivated by selected chelators.
Schiff Bases such as N,N'-salicylidene-1,2-diamino-propane are the most commonly used metal de, activators. In U.S. Pat. Nos. 3,034,876 and 3,068,083, the use of this Schiff Base with esters were claimed as synergistic blends for the thermal stabilization of jet fuels. Gonzalez, in U.S. Pat. Nos. 3,437,583 and 3,442,791, claims the use of N,N'-disalicylidene-1,2-diaminopropane in combination with the product from the reaction of a phenol, an amine, and an aldehyde as a synergistic antifoulant. Alone the product of reaction of the phenol, mine, and aldehyde had little, if any, antifoulant activity.
Products from the reaction of a phenol, an mine, and an aldehyde (known as Mannich-type products) have been prepared in many ways with differing results due to the method of preparation and due to the exact ratio of reactants and the structure of the reactants.
Metal chelators were prepared by a Mannich reaction in U.S. Pat. No. 3,355,270. Such chelators were reacted with iron to form a metallic chelate complex which metallic complex was then added to the furnace oil as a catalyst to enhance combustion. The activity of the iron was not decreased or deactivated by the hyphenate chelator.
Sargent et at. U.S. Pat. No. 2,353,192, and Otto, U.S. Pat. No. 3,368,972, teach that Mannich products can be prepared from alkyl substituted catechols. However, such products are not actually prepared. The alkylphenol Mannich products that are prepared in these two patents are used in finished products, where detectable amounts of transition metals are initially absent, as stabilizers against oxidation.
Mannich-type products were used as dispersants in U.S. Pat. No. 3,235,484, U.S. Pat. No. Re. 26,330, U.S. Pat. Nos. 4,032,304 and 4,200,545. A Mannich-type product in combination with a polyalkylene amine was used to provide stability in preventing thermal degradation of fuels in U.S. Pat. No. 4,166,726.
Copper, but not iron, is effectively deactivated by metal chelators such as N,N'-disalicylidene-1,2-diaminopropane. Mannich-type products, while acting as chelators for the preparation of catalysts or as dispersants, have been shown to be iron ion deactivators in U.S. Pat. Nos. 5,271,863, 4,883,580 and 4,847,415.